diff --git a/MPChartLib/src/main/java/com/github/mikephil/charting/charts/HorizontalBarChart.java b/MPChartLib/src/main/java/com/github/mikephil/charting/charts/HorizontalBarChart.java
index cc1ac21f7..93c78295d 100644
--- a/MPChartLib/src/main/java/com/github/mikephil/charting/charts/HorizontalBarChart.java
+++ b/MPChartLib/src/main/java/com/github/mikephil/charting/charts/HorizontalBarChart.java
@@ -224,11 +224,6 @@ public void getBarBounds(BarEntry barEntry, RectF outputRect) {
 		RectF bounds = outputRect;
 		IBarDataSet set = mData.getDataSetForEntry(barEntry);
 
-		if (set == null) {
-			outputRect.set(Float.MIN_VALUE, Float.MIN_VALUE, Float.MIN_VALUE, Float.MIN_VALUE);
-			return;
-		}
-
 		float y = barEntry.getY();
 		float x = barEntry.getX();
 
diff --git a/MPChartLib/src/main/java/com/github/mikephil/charting/components/Legend.kt b/MPChartLib/src/main/java/com/github/mikephil/charting/components/Legend.kt
index a8596b132..4b0d4b9f5 100644
--- a/MPChartLib/src/main/java/com/github/mikephil/charting/components/Legend.kt
+++ b/MPChartLib/src/main/java/com/github/mikephil/charting/components/Legend.kt
@@ -18,7 +18,6 @@ import kotlin.collections.MutableList
 import kotlin.collections.toTypedArray
 import kotlin.math.max
 import kotlin.math.min
-import kotlin.requireNotNull
 
 /**
  * Class representing the legend of the chart. The legend will contain one entry
@@ -87,10 +86,6 @@ class Legend() : ComponentBase() {
     var extraEntries: Array<LegendEntry> = arrayOf<LegendEntry>()
         private set
 
-    /**
-     * @return true if a custom legend entries has been set default
-     * false (automatic legend)
-     */
     /**
      * Are the legend labels/colors a custom value or auto calculated? If false,
      * then it's auto, if true, then custom. default false (automatic legend)
@@ -98,23 +93,14 @@ class Legend() : ComponentBase() {
     var isLegendCustom: Boolean = false
         private set
 
-    /**
-     * returns the horizontal alignment of the legend
-     */
     /**
      * sets the horizontal alignment of the legend
      */
-    var horizontalAlignment: LegendHorizontalAlignment? = LegendHorizontalAlignment.LEFT
-    /**
-     * returns the vertical alignment of the legend
-     */
+    var horizontalAlignment: LegendHorizontalAlignment = LegendHorizontalAlignment.LEFT
     /**
      * sets the vertical alignment of the legend
      */
-    var verticalAlignment: LegendVerticalAlignment? = LegendVerticalAlignment.BOTTOM
-    /**
-     * returns the orientation of the legend
-     */
+    var verticalAlignment: LegendVerticalAlignment = LegendVerticalAlignment.BOTTOM
     /**
      * sets the orientation of the legend
      */
@@ -126,93 +112,41 @@ class Legend() : ComponentBase() {
     var isDrawInsideEnabled: Boolean = false
         private set
 
-    /**
-     * returns the text direction of the legend
-     */
-    /**
-     * sets the text direction of the legend
-     */
     /**
      * the text direction for the legend
      */
-    var direction: LegendDirection? = LegendDirection.LEFT_TO_RIGHT
+    var direction: LegendDirection = LegendDirection.LEFT_TO_RIGHT
 
-    /**
-     * returns the current form/shape that is set for the legend
-     */
-    /**
-     * sets the form/shape of the legend forms
-     */
     /**
      * the shape/form the legend colors are drawn in
      */
-    var form: LegendForm? = LegendForm.SQUARE
+    var form: LegendForm = LegendForm.SQUARE
 
-    /**
-     * returns the size in dp of the legend forms
-     */
-    /**
-     * sets the size in dp of the legend forms, default 8f
-     */
     /**
      * the size of the legend forms/shapes
      */
     var formSize: kotlin.Float = 8f
 
-    /**
-     * returns the line width in dp for drawing forms that consist of lines
-     */
-    /**
-     * sets the line width in dp for forms that consist of lines, default 3f
-     */
     /**
      * the size of the legend forms/shapes
      */
     var formLineWidth: kotlin.Float = 3f
 
-    /**
-     * @return The line dash path effect used for shapes that consist of lines.
-     */
-    /**
-     * Sets the line dash path effect used for shapes that consist of lines.
-     */
     /**
      * Line dash path effect used for shapes that consist of lines.
      */
     var formLineDashEffect: DashPathEffect? = null
 
-    /**
-     * returns the space between the legend entries on a horizontal axis in
-     * pixels
-     */
-    /**
-     * sets the space between the legend entries on a horizontal axis in pixels,
-     * converts to dp internally
-     */
     /**
      * the space between the legend entries on a horizontal axis, default 6f
      */
     var xEntrySpace: kotlin.Float = 6f
 
-    /**
-     * returns the space between the legend entries on a vertical axis in pixels
-     */
-    /**
-     * sets the space between the legend entries on a vertical axis in pixels,
-     * converts to dp internally
-     */
     /**
      * the space between the legend entries on a vertical axis, default 5f
      */
     var yEntrySpace: kotlin.Float = 0f
 
-    /**
-     * returns the space between the form and the actual label/text
-     */
-    /**
-     * sets the space between the form and the actual label/text, converts to dp
-     * internally
-     */
     /**
      * the space between the legend entries on a vertical axis, default 2f
      * private float mYEntrySpace = 2f; / ** the space between the form and the
@@ -220,12 +154,6 @@ class Legend() : ComponentBase() {
      */
     var formToTextSpace: kotlin.Float = 5f
 
-    /**
-     * returns the space that is left out between stacked forms (with no label)
-     */
-    /**
-     * sets the space that is left out between stacked forms (with no label)
-     */
     /**
      * the space that should be left between stacked forms
      */
@@ -239,23 +167,12 @@ class Legend() : ComponentBase() {
      * piechart, then this defines the size of the rectangular bounds out of the
      * size of the "hole". / default: 0.95f (95%)
      */
-    /**
-     * The maximum relative size out of the whole chart view. / If
-     * the legend is to the right/left of the chart, then this affects the width
-     * of the legend. / If the legend is to the top/bottom of the chart, then
-     * this affects the height of the legend. / default: 0.95f (95%)
-     */
-    /**
-     * the maximum relative size out of the whole chart view in percent
-     */
     var maxSizePercent: kotlin.Float = 0.95f
 
     /**
      * Constructor. Provide entries for the legend.
      */
     constructor(entries: Array<LegendEntry>) : this() {
-        requireNotNull(entries) { "entries array is NULL" }
-
         this.entries = entries
     }
 
diff --git a/MPChartLib/src/main/java/com/github/mikephil/charting/components/LegendEntry.kt b/MPChartLib/src/main/java/com/github/mikephil/charting/components/LegendEntry.kt
index c435a1d2c..c0aafe36b 100644
--- a/MPChartLib/src/main/java/com/github/mikephil/charting/components/LegendEntry.kt
+++ b/MPChartLib/src/main/java/com/github/mikephil/charting/components/LegendEntry.kt
@@ -19,7 +19,7 @@ class LegendEntry {
      */
     constructor(
         label: String?,
-        form: LegendForm?,
+        form: LegendForm,
         formSize: Float,
         formLineWidth: Float,
         formLineDashEffect: DashPathEffect?,
@@ -46,7 +46,7 @@ class LegendEntry {
      * `EMPTY` will avoid drawing a form, but keep its space.
      * `DEFAULT` will use the Legend's default.
      */
-    var form: LegendForm? = LegendForm.DEFAULT
+    var form: LegendForm = LegendForm.DEFAULT
 
     /**
      * Form size will be considered except for when .None is used
diff --git a/MPChartLib/src/main/java/com/github/mikephil/charting/listener/PieRadarChartTouchListener.kt b/MPChartLib/src/main/java/com/github/mikephil/charting/listener/PieRadarChartTouchListener.kt
index 8fcae2d89..2b127de47 100644
--- a/MPChartLib/src/main/java/com/github/mikephil/charting/listener/PieRadarChartTouchListener.kt
+++ b/MPChartLib/src/main/java/com/github/mikephil/charting/listener/PieRadarChartTouchListener.kt
@@ -65,7 +65,7 @@ class PieRadarChartTouchListener(chart: PieRadarChartBase<*>?) : ChartTouchListe
                         chart!!.disableScroll()
                     } else if (touchMode == ROTATE) {
                         updateGestureRotation(x, y)
-                        chart!!.invalidate()
+                        chart?.invalidate()
                     }
 
                     endAction(event)
diff --git a/MPChartLib/src/main/java/com/github/mikephil/charting/renderer/LegendRenderer.kt b/MPChartLib/src/main/java/com/github/mikephil/charting/renderer/LegendRenderer.kt
index 2799b6c96..7d9e190af 100644
--- a/MPChartLib/src/main/java/com/github/mikephil/charting/renderer/LegendRenderer.kt
+++ b/MPChartLib/src/main/java/com/github/mikephil/charting/renderer/LegendRenderer.kt
@@ -4,7 +4,6 @@ import android.graphics.Canvas
 import android.graphics.Paint
 import android.graphics.Paint.Align
 import android.graphics.Path
-import android.util.Log
 import androidx.core.graphics.withSave
 import com.github.mikephil.charting.components.Legend
 import com.github.mikephil.charting.components.Legend.LegendDirection
@@ -228,7 +227,7 @@ open class LegendRenderer(
 
         val yOffset = legend.yOffset
         val xOffset = legend.xOffset
-        var originPosX = 0f
+        var originPosX: Float
 
         when (horizontalAlignment) {
             LegendHorizontalAlignment.LEFT -> {
@@ -266,8 +265,6 @@ open class LegendRenderer(
                         legend.mNeededWidth / 2.0 - xOffset).toFloat()
                 }
             }
-
-            null -> Log.e("Chart", "Legend horizontalAlignment is null")
         }
 
         when (orientation) {
@@ -282,10 +279,6 @@ open class LegendRenderer(
                     LegendVerticalAlignment.TOP -> yOffset
                     LegendVerticalAlignment.BOTTOM -> viewPortHandler.chartHeight - yOffset - legend.mNeededHeight
                     LegendVerticalAlignment.CENTER -> (viewPortHandler.chartHeight - legend.mNeededHeight) / 2f + yOffset
-                    else -> {
-                        Log.w("Chart", "Legend verticalAlignment not set")
-                        0f
-                    }
                 }
 
                 var lineIndex = 0
@@ -344,7 +337,7 @@ open class LegendRenderer(
                 // contains the stacked legend size in pixels
                 var stack = 0f
                 var wasStacked = false
-                var posY = 0f
+                var posY: Float
 
                 when (verticalAlignment) {
                     LegendVerticalAlignment.TOP -> {
@@ -366,8 +359,6 @@ open class LegendRenderer(
                     LegendVerticalAlignment.CENTER -> posY = (viewPortHandler.chartHeight / 2f
                             - legend.mNeededHeight / 2f
                             + legend.yOffset)
-
-                    null -> Log.w("Chart", "Legend verticalAlignment is null")
                 }
 
                 var i = 0
@@ -496,9 +487,6 @@ open class LegendRenderer(
                     mLineFormPath.lineTo(x + formSize, y)
                     canvas.drawPath(mLineFormPath, formPaint)
                 }
-
-                null -> Log.w( "Chart", "Legend form is null")
-
             }
 
         }
diff --git a/app/src/main/kotlin/info/appdev/chartexample/AnotherBarActivity.kt b/app/src/main/kotlin/info/appdev/chartexample/AnotherBarActivity.kt
index 4e67247fe..75c3e7c12 100644
--- a/app/src/main/kotlin/info/appdev/chartexample/AnotherBarActivity.kt
+++ b/app/src/main/kotlin/info/appdev/chartexample/AnotherBarActivity.kt
@@ -92,7 +92,7 @@ class AnotherBarActivity : DemoBase(), OnSeekBarChangeListener {
             set1 = chart!!.data!!.getDataSetByIndex(0) as BarDataSet
             set1.entries = values
             chart!!.data!!.notifyDataChanged()
-            chart!!.notifyDataSetChanged()
+            chart?.notifyDataSetChanged()
         } else {
             set1 = BarDataSet(values, "Data Set")
             set1.setColors(*ColorTemplate.VORDIPLOM_COLORS)
@@ -106,7 +106,7 @@ class AnotherBarActivity : DemoBase(), OnSeekBarChangeListener {
             chart!!.setFitBars(true)
         }
 
-        chart!!.invalidate()
+        chart?.invalidate()
     }
 
     override fun onCreateOptionsMenu(menu: Menu): Boolean {
@@ -128,13 +128,13 @@ class AnotherBarActivity : DemoBase(), OnSeekBarChangeListener {
                     it?.isDrawValues = !it.isDrawValues
                 }
 
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleHighlight -> {
                 if (chart!!.data != null) {
                     chart!!.data!!.isHighlightEnabled = !chart!!.data!!.isHighlightEnabled()
-                    chart!!.invalidate()
+                    chart?.invalidate()
                 }
             }
 
@@ -142,18 +142,18 @@ class AnotherBarActivity : DemoBase(), OnSeekBarChangeListener {
                 if (chart!!.isPinchZoomEnabled) chart!!.setPinchZoom(false)
                 else chart!!.setPinchZoom(true)
 
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleAutoScaleMinMax -> {
                 chart!!.isAutoScaleMinMaxEnabled = !chart!!.isAutoScaleMinMaxEnabled
-                chart!!.notifyDataSetChanged()
+                chart?.notifyDataSetChanged()
             }
 
             R.id.actionToggleBarBorders -> {
                 for (set in chart!!.data!!.dataSets) (set as BarDataSet).barBorderWidth = if (set.barBorderWidth == 1f) 0f else 1f
 
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.animateX -> {
diff --git a/app/src/main/kotlin/info/appdev/chartexample/BarChartActivity.kt b/app/src/main/kotlin/info/appdev/chartexample/BarChartActivity.kt
index 661c0f064..9cde1a234 100644
--- a/app/src/main/kotlin/info/appdev/chartexample/BarChartActivity.kt
+++ b/app/src/main/kotlin/info/appdev/chartexample/BarChartActivity.kt
@@ -115,7 +115,7 @@ class BarChartActivity : DemoBase(), OnSeekBarChangeListener, OnChartValueSelect
 
         val mv = XYMarkerView(this, xAxisFormatter)
         mv.chartView = chart // For bounds control
-        chart!!.setMarker(mv) // Set the marker to the chart
+        chart?.setMarker(mv) // Set the marker to the chart
 
         // setting data
         seekBarY!!.progress = 50
@@ -150,7 +150,7 @@ class BarChartActivity : DemoBase(), OnSeekBarChangeListener, OnChartValueSelect
             set1 = chart!!.data!!.getDataSetByIndex(0) as BarDataSet
             set1.entries  = values
             chart!!.data!!.notifyDataChanged()
-            chart!!.notifyDataSetChanged()
+            chart?.notifyDataSetChanged()
         } else {
             set1 = BarDataSet(values, "The year 2017")
 
@@ -184,7 +184,7 @@ class BarChartActivity : DemoBase(), OnSeekBarChangeListener, OnChartValueSelect
             data.setValueTypeface(tfLight)
             data.barWidth = 0.9f
 
-            chart!!.setData(data)
+            chart?.setData(data)
         }
     }
 
@@ -206,20 +206,20 @@ class BarChartActivity : DemoBase(), OnSeekBarChangeListener, OnChartValueSelect
                     it?.isDrawValues = !it.isDrawValues
                 }
 
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleIcons -> {
                 for (set in chart!!.data!!.dataSets)
                     set?.isDrawIcons = !set.isDrawIcons
 
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleHighlight -> {
                 if (chart!!.data != null) {
                     chart!!.data!!.isHighlightEnabled = !chart!!.data!!.isHighlightEnabled()
-                    chart!!.invalidate()
+                    chart?.invalidate()
                 }
             }
 
@@ -227,12 +227,12 @@ class BarChartActivity : DemoBase(), OnSeekBarChangeListener, OnChartValueSelect
                 if (chart!!.isPinchZoomEnabled) chart!!.setPinchZoom(false)
                 else chart!!.setPinchZoom(true)
 
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleAutoScaleMinMax -> {
                 chart!!.isAutoScaleMinMaxEnabled = !chart!!.isAutoScaleMinMaxEnabled
-                chart!!.notifyDataSetChanged()
+                chart?.notifyDataSetChanged()
             }
 
             R.id.actionToggleBarBorders -> {
@@ -242,7 +242,7 @@ class BarChartActivity : DemoBase(), OnSeekBarChangeListener, OnChartValueSelect
                     else
                         1f
 
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.animateX -> {
@@ -267,8 +267,8 @@ class BarChartActivity : DemoBase(), OnSeekBarChangeListener, OnChartValueSelect
 
             R.id.actionRotateXAxisLabelsBy45Deg -> {
                 chart!!.xAxis.labelRotationAngle = 45f
-                chart!!.notifyDataSetChanged()
-                chart!!.invalidate()
+                chart?.notifyDataSetChanged()
+                chart?.invalidate()
             }
         }
         return true
@@ -279,7 +279,7 @@ class BarChartActivity : DemoBase(), OnSeekBarChangeListener, OnChartValueSelect
         tvY!!.text = seekBarY!!.progress.toString()
 
         setData(seekBarX!!.progress, seekBarY!!.progress.toFloat())
-        chart!!.invalidate()
+        chart?.invalidate()
     }
 
     override fun saveToGallery() {
diff --git a/app/src/main/kotlin/info/appdev/chartexample/BarChartActivityMultiDataset.kt b/app/src/main/kotlin/info/appdev/chartexample/BarChartActivityMultiDataset.kt
index 0d6cc3a33..209f4c2b0 100644
--- a/app/src/main/kotlin/info/appdev/chartexample/BarChartActivityMultiDataset.kt
+++ b/app/src/main/kotlin/info/appdev/chartexample/BarChartActivityMultiDataset.kt
@@ -147,7 +147,7 @@ class BarChartActivityMultiDataset : DemoBase(), OnSeekBarChangeListener, OnChar
             set3.entries = values3
             set4.entries = values4
             chart!!.data!!.notifyDataChanged()
-            chart!!.notifyDataSetChanged()
+            chart?.notifyDataSetChanged()
         } else {
             // create 4 DataSets
             set1 = BarDataSet(values1, "Company A")
@@ -175,7 +175,7 @@ class BarChartActivityMultiDataset : DemoBase(), OnSeekBarChangeListener, OnChar
         // barData.getGroupWith(...) is a helper that calculates the width each group needs based on the provided parameters
         chart!!.xAxis.axisMaximum = startYear + chart!!.barData.getGroupWidth(groupSpace, barSpace) * groupCount
         chart!!.groupBars(startYear.toFloat(), groupSpace, barSpace)
-        chart!!.invalidate()
+        chart?.invalidate()
     }
 
     override fun onCreateOptionsMenu(menu: Menu?): Boolean {
@@ -197,31 +197,31 @@ class BarChartActivityMultiDataset : DemoBase(), OnSeekBarChangeListener, OnChar
                     it?.isDrawValues = !it.isDrawValues
                 }
 
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionTogglePinch -> {
                 if (chart!!.isPinchZoomEnabled) chart!!.setPinchZoom(false)
                 else chart!!.setPinchZoom(true)
 
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleAutoScaleMinMax -> {
                 chart!!.isAutoScaleMinMaxEnabled = !chart!!.isAutoScaleMinMaxEnabled
-                chart!!.notifyDataSetChanged()
+                chart?.notifyDataSetChanged()
             }
 
             R.id.actionToggleBarBorders -> {
                 for (set in chart!!.data!!.dataSets) (set as BarDataSet).barBorderWidth = if (set.barBorderWidth == 1f) 0f else 1f
 
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleHighlight -> {
                 if (chart!!.data != null) {
                     chart!!.data!!.isHighlightEnabled = !chart!!.data!!.isHighlightEnabled()
-                    chart!!.invalidate()
+                    chart?.invalidate()
                 }
             }
 
diff --git a/app/src/main/kotlin/info/appdev/chartexample/BarChartPositiveNegative.kt b/app/src/main/kotlin/info/appdev/chartexample/BarChartPositiveNegative.kt
index 2689fb268..78b511c1b 100644
--- a/app/src/main/kotlin/info/appdev/chartexample/BarChartPositiveNegative.kt
+++ b/app/src/main/kotlin/info/appdev/chartexample/BarChartPositiveNegative.kt
@@ -110,7 +110,7 @@ class BarChartPositiveNegative : DemoBase() {
             set = chart!!.data!!.getDataSetByIndex(0) as BarDataSet
             set.entries  = values
             chart!!.data!!.notifyDataChanged()
-            chart!!.notifyDataSetChanged()
+            chart?.notifyDataSetChanged()
         } else {
             set = BarDataSet(values, "Values")
             set.setColors(colors)
@@ -123,7 +123,7 @@ class BarChartPositiveNegative : DemoBase() {
             data.barWidth = 0.8f
 
             chart!!.setData(data)
-            chart!!.invalidate()
+            chart?.invalidate()
         }
     }
 
diff --git a/app/src/main/kotlin/info/appdev/chartexample/BubbleChartActivity.kt b/app/src/main/kotlin/info/appdev/chartexample/BubbleChartActivity.kt
index 16388d3be..9c0a70d42 100644
--- a/app/src/main/kotlin/info/appdev/chartexample/BubbleChartActivity.kt
+++ b/app/src/main/kotlin/info/appdev/chartexample/BubbleChartActivity.kt
@@ -150,7 +150,7 @@ class BubbleChartActivity : DemoBase(), OnSeekBarChangeListener, OnChartValueSel
         data.setHighlightCircleWidth(1.5f)
 
         chart!!.setData(data)
-        chart!!.invalidate()
+        chart?.invalidate()
     }
 
     override fun onCreateOptionsMenu(menu: Menu?): Boolean {
@@ -170,19 +170,19 @@ class BubbleChartActivity : DemoBase(), OnSeekBarChangeListener, OnChartValueSel
                 chart!!.data!!.dataSets.forEach {
                     it?.isDrawValues = !it.isDrawValues
                 }
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleIcons -> {
                 for (set in chart!!.data!!.dataSets)
                     set?.isDrawIcons = !set.isDrawIcons
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleHighlight -> {
                 if (chart!!.data != null) {
                     chart!!.data!!.isHighlightEnabled = !chart!!.data!!.isHighlightEnabled()
-                    chart!!.invalidate()
+                    chart?.invalidate()
                 }
             }
 
@@ -190,12 +190,12 @@ class BubbleChartActivity : DemoBase(), OnSeekBarChangeListener, OnChartValueSel
                 if (chart!!.isPinchZoomEnabled) chart!!.setPinchZoom(false)
                 else chart!!.setPinchZoom(true)
 
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleAutoScaleMinMax -> {
                 chart!!.isAutoScaleMinMaxEnabled = !chart!!.isAutoScaleMinMaxEnabled
-                chart!!.notifyDataSetChanged()
+                chart?.notifyDataSetChanged()
             }
 
             R.id.actionSave -> {
diff --git a/app/src/main/kotlin/info/appdev/chartexample/CandleStickChartActivity.kt b/app/src/main/kotlin/info/appdev/chartexample/CandleStickChartActivity.kt
index 412f83ca2..da76c3a35 100644
--- a/app/src/main/kotlin/info/appdev/chartexample/CandleStickChartActivity.kt
+++ b/app/src/main/kotlin/info/appdev/chartexample/CandleStickChartActivity.kt
@@ -130,7 +130,7 @@ class CandleStickChartActivity : DemoBase(), OnSeekBarChangeListener {
         val data = CandleData(set1)
 
         chart!!.setData(data)
-        chart!!.invalidate()
+        chart?.invalidate()
     }
 
     override fun onCreateOptionsMenu(menu: Menu?): Boolean {
@@ -151,19 +151,19 @@ class CandleStickChartActivity : DemoBase(), OnSeekBarChangeListener {
                 chart!!.data!!.dataSets.forEach {
                     it?.isDrawValues = !it.isDrawValues
                 }
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleIcons -> {
                 for (set in chart!!.data!!.dataSets)
                     set?.isDrawIcons = !set.isDrawIcons
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleHighlight -> {
                 if (chart!!.data != null) {
                     chart!!.data!!.isHighlightEnabled = !chart!!.data!!.isHighlightEnabled()
-                    chart!!.invalidate()
+                    chart?.invalidate()
                 }
             }
 
@@ -171,12 +171,12 @@ class CandleStickChartActivity : DemoBase(), OnSeekBarChangeListener {
                 if (chart!!.isPinchZoomEnabled) chart!!.setPinchZoom(false)
                 else chart!!.setPinchZoom(true)
 
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleAutoScaleMinMax -> {
                 chart!!.isAutoScaleMinMaxEnabled = !chart!!.isAutoScaleMinMaxEnabled
-                chart!!.notifyDataSetChanged()
+                chart?.notifyDataSetChanged()
             }
 
             R.id.actionToggleMakeShadowSameColorAsCandle -> {
@@ -184,7 +184,7 @@ class CandleStickChartActivity : DemoBase(), OnSeekBarChangeListener {
                     (set as CandleDataSet).shadowColorSameAsCandle = !set.shadowColorSameAsCandle
                 }
 
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.animateX -> {
diff --git a/app/src/main/kotlin/info/appdev/chartexample/CombinedChartActivity.kt b/app/src/main/kotlin/info/appdev/chartexample/CombinedChartActivity.kt
index 7871e499f..83a5a6d27 100644
--- a/app/src/main/kotlin/info/appdev/chartexample/CombinedChartActivity.kt
+++ b/app/src/main/kotlin/info/appdev/chartexample/CombinedChartActivity.kt
@@ -93,7 +93,7 @@ class CombinedChartActivity : DemoBase() {
         xAxis.axisMaximum = data.xMax + 0.25f
 
         chart!!.setData(data)
-        chart!!.invalidate()
+        chart?.invalidate()
     }
 
     private fun generateLineData(): LineData {
@@ -242,7 +242,7 @@ class CombinedChartActivity : DemoBase() {
                     if (it is LineDataSet)
                         it.isDrawValues = !it.isDrawValues
                 }
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleBarValues -> {
@@ -250,15 +250,15 @@ class CombinedChartActivity : DemoBase() {
                     if (it is BarDataSet)
                         it.isDrawValues = !it.isDrawValues
                 }
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionRemoveDataSet -> {
                 val rnd = values[sampleCount]!!.toFloat().toInt() * chart!!.data!!.getDataSetCount()
                 chart!!.data!!.removeDataSet(chart!!.data!!.getDataSetByIndex(rnd))
                 chart!!.data!!.notifyDataChanged()
-                chart!!.notifyDataSetChanged()
-                chart!!.invalidate()
+                chart?.notifyDataSetChanged()
+                chart?.invalidate()
             }
         }
         return true
diff --git a/app/src/main/kotlin/info/appdev/chartexample/DynamicalAddingActivity.kt b/app/src/main/kotlin/info/appdev/chartexample/DynamicalAddingActivity.kt
index 3c82c0222..7ac0a78e2 100644
--- a/app/src/main/kotlin/info/appdev/chartexample/DynamicalAddingActivity.kt
+++ b/app/src/main/kotlin/info/appdev/chartexample/DynamicalAddingActivity.kt
@@ -37,7 +37,7 @@ class DynamicalAddingActivity : DemoBase(), OnChartValueSelectedListener {
 
         //        chart.getXAxis().setDrawLabels(false);
 //        chart.getXAxis().setDrawGridLines(false);
-        chart!!.invalidate()
+        chart?.invalidate()
     }
 
     private val colors: IntArray = ColorTemplate.VORDIPLOM_COLORS
@@ -69,7 +69,7 @@ class DynamicalAddingActivity : DemoBase(), OnChartValueSelectedListener {
             data.notifyDataChanged()
 
             // let the chart know it's data has changed
-            chart!!.notifyDataSetChanged()
+            chart?.notifyDataSetChanged()
 
             chart!!.setVisibleXRangeMaximum(6f)
             //chart.setVisibleYRangeMaximum(15, AxisDependency.LEFT);
@@ -92,8 +92,8 @@ class DynamicalAddingActivity : DemoBase(), OnChartValueSelectedListener {
                 // or remove by index
                 // mData.removeEntryByXValue(xIndex, dataSetIndex);
                 data.notifyDataChanged()
-                chart!!.notifyDataSetChanged()
-                chart!!.invalidate()
+                chart?.notifyDataSetChanged()
+                chart?.invalidate()
             }
         }
     }
@@ -129,8 +129,8 @@ class DynamicalAddingActivity : DemoBase(), OnChartValueSelectedListener {
 
             data.addDataSet(set)
             data.notifyDataChanged()
-            chart!!.notifyDataSetChanged()
-            chart!!.invalidate()
+            chart?.notifyDataSetChanged()
+            chart?.invalidate()
         }
     }
 
@@ -140,8 +140,8 @@ class DynamicalAddingActivity : DemoBase(), OnChartValueSelectedListener {
         if (data != null) {
             data.removeDataSet(data.getDataSetByIndex(data.getDataSetCount() - 1))
 
-            chart!!.notifyDataSetChanged()
-            chart!!.invalidate()
+            chart?.notifyDataSetChanged()
+            chart?.invalidate()
         }
     }
 
diff --git a/app/src/main/kotlin/info/appdev/chartexample/HalfPieChartActivity.kt b/app/src/main/kotlin/info/appdev/chartexample/HalfPieChartActivity.kt
index c9e984bfd..9dfa6cd91 100644
--- a/app/src/main/kotlin/info/appdev/chartexample/HalfPieChartActivity.kt
+++ b/app/src/main/kotlin/info/appdev/chartexample/HalfPieChartActivity.kt
@@ -102,7 +102,7 @@ class HalfPieChartActivity : DemoBase() {
         data.setValueTypeface(tfLight)
         chart!!.setData(data)
 
-        chart!!.invalidate()
+        chart?.invalidate()
     }
 
     private fun generateCenterSpannableText(): SpannableString {
diff --git a/app/src/main/kotlin/info/appdev/chartexample/HorizontalBarNegativeChartActivity.kt b/app/src/main/kotlin/info/appdev/chartexample/HorizontalBarNegativeChartActivity.kt
index c9300b99b..0b6171ddc 100644
--- a/app/src/main/kotlin/info/appdev/chartexample/HorizontalBarNegativeChartActivity.kt
+++ b/app/src/main/kotlin/info/appdev/chartexample/HorizontalBarNegativeChartActivity.kt
@@ -128,7 +128,7 @@ class HorizontalBarNegativeChartActivity : DemoBase(), OnSeekBarChangeListener,
             set1 = chart!!.data!!.getDataSetByIndex(0) as BarDataSet
             set1.entries  = values
             chart!!.data!!.notifyDataChanged()
-            chart!!.notifyDataSetChanged()
+            chart?.notifyDataSetChanged()
         } else {
             set1 = BarDataSet(values, "DataSet 1")
 
@@ -163,7 +163,7 @@ class HorizontalBarNegativeChartActivity : DemoBase(), OnSeekBarChangeListener,
                 chart!!.data!!.dataSets.forEach {
                     it?.isDrawValues = !it.isDrawValues
                 }
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleIcons -> {
@@ -171,31 +171,31 @@ class HorizontalBarNegativeChartActivity : DemoBase(), OnSeekBarChangeListener,
                     iSet.isDrawIcons = !iSet.isDrawIcons
                 }
 
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleHighlight -> {
                 if (chart!!.data != null) {
                     chart!!.data!!.isHighlightEnabled = !chart!!.data!!.isHighlightEnabled()
-                    chart!!.invalidate()
+                    chart?.invalidate()
                 }
             }
 
             R.id.actionTogglePinch -> {
                 chart!!.setPinchZoom(!chart!!.isPinchZoomEnabled)
 
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleAutoScaleMinMax -> {
                 chart!!.isAutoScaleMinMaxEnabled = !chart!!.isAutoScaleMinMaxEnabled
-                chart!!.notifyDataSetChanged()
+                chart?.notifyDataSetChanged()
             }
 
             R.id.actionToggleBarBorders -> {
                 for (set in chart!!.data!!.dataSets) (set as BarDataSet).barBorderWidth = if (set.barBorderWidth == 1f) 0f else 1f
 
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.animateX -> {
@@ -227,7 +227,7 @@ class HorizontalBarNegativeChartActivity : DemoBase(), OnSeekBarChangeListener,
 
         setData(seekBarX!!.progress, seekBarY!!.progress.toFloat())
         chart!!.setFitBars(true)
-        chart!!.invalidate()
+        chart?.invalidate()
     }
 
     override fun saveToGallery() {
diff --git a/app/src/main/kotlin/info/appdev/chartexample/InvertedLineChartActivity.kt b/app/src/main/kotlin/info/appdev/chartexample/InvertedLineChartActivity.kt
index f4b4bfcbd..72635d44b 100644
--- a/app/src/main/kotlin/info/appdev/chartexample/InvertedLineChartActivity.kt
+++ b/app/src/main/kotlin/info/appdev/chartexample/InvertedLineChartActivity.kt
@@ -99,7 +99,7 @@ class InvertedLineChartActivity : DemoBase(), OnSeekBarChangeListener, OnChartVa
         l.form = LegendForm.LINE
 
         // don't forget to refresh the drawing
-        chart!!.invalidate()
+        chart?.invalidate()
     }
 
     private fun setData(count: Int, range: Float) {
@@ -146,13 +146,13 @@ class InvertedLineChartActivity : DemoBase(), OnSeekBarChangeListener, OnChartVa
                 chart!!.data!!.dataSets.forEach {
                     it?.isDrawValues = !it.isDrawValues
                 }
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleHighlight -> {
                 if (chart!!.data != null) {
                     chart!!.data!!.isHighlightEnabled = !chart!!.data!!.isHighlightEnabled()
-                    chart!!.invalidate()
+                    chart?.invalidate()
                 }
             }
 
@@ -160,7 +160,7 @@ class InvertedLineChartActivity : DemoBase(), OnSeekBarChangeListener, OnChartVa
                 chart!!.data!!.dataSets.forEach { set ->
                     set?.setDrawFilled(!set.isDrawFilledEnabled)
                 }
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleCircles -> {
@@ -170,7 +170,7 @@ class InvertedLineChartActivity : DemoBase(), OnSeekBarChangeListener, OnChartVa
                     val set = iSet as LineDataSet
                     set.isDrawCirclesEnabled = !set.isDrawCirclesEnabled
                 }
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.animateX -> {
@@ -188,12 +188,12 @@ class InvertedLineChartActivity : DemoBase(), OnSeekBarChangeListener, OnChartVa
             R.id.actionTogglePinch -> {
                 chart!!.setPinchZoom(!chart!!.isPinchZoomEnabled)
 
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleAutoScaleMinMax -> {
                 chart!!.isAutoScaleMinMaxEnabled = !chart!!.isAutoScaleMinMaxEnabled
-                chart!!.notifyDataSetChanged()
+                chart?.notifyDataSetChanged()
             }
 
             R.id.actionSave -> {
@@ -214,7 +214,7 @@ class InvertedLineChartActivity : DemoBase(), OnSeekBarChangeListener, OnChartVa
         setData(seekBarX!!.progress, seekBarY!!.progress.toFloat())
 
         // redraw
-        chart!!.invalidate()
+        chart?.invalidate()
     }
 
     override fun saveToGallery() {
diff --git a/app/src/main/kotlin/info/appdev/chartexample/LineChartDualAxisActivity.kt b/app/src/main/kotlin/info/appdev/chartexample/LineChartDualAxisActivity.kt
index 311fa7cb6..2a161d1e6 100644
--- a/app/src/main/kotlin/info/appdev/chartexample/LineChartDualAxisActivity.kt
+++ b/app/src/main/kotlin/info/appdev/chartexample/LineChartDualAxisActivity.kt
@@ -157,7 +157,7 @@ class LineChartDualAxisActivity : DemoBase(), OnSeekBarChangeListener, OnChartVa
             set2.entries = values2
             set3.entries = values3
             chart!!.data!!.notifyDataChanged()
-            chart!!.notifyDataSetChanged()
+            chart?.notifyDataSetChanged()
         } else {
             // create a dataset and give it a type
             set1 = LineDataSet(values1, "DataSet 1")
@@ -229,13 +229,13 @@ class LineChartDualAxisActivity : DemoBase(), OnSeekBarChangeListener, OnChartVa
                 chart!!.data!!.dataSets.forEach { set ->
                     set?.isDrawValues = !set.isDrawValues
                 }
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleHighlight -> {
                 if (chart!!.data != null) {
                     chart!!.data!!.isHighlightEnabled = !chart!!.data!!.isHighlightEnabled()
-                    chart!!.invalidate()
+                    chart?.invalidate()
                 }
             }
 
@@ -243,7 +243,7 @@ class LineChartDualAxisActivity : DemoBase(), OnSeekBarChangeListener, OnChartVa
                 chart!!.data!!.dataSets.forEach { set ->
                     set?.setDrawFilled(!set.isDrawFilledEnabled)
                 }
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleCircles -> {
@@ -253,7 +253,7 @@ class LineChartDualAxisActivity : DemoBase(), OnSeekBarChangeListener, OnChartVa
                     val set = iSet as LineDataSet
                     set.isDrawCirclesEnabled = !set.isDrawCirclesEnabled
                 }
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleCubic -> {
@@ -266,7 +266,7 @@ class LineChartDualAxisActivity : DemoBase(), OnSeekBarChangeListener, OnChartVa
                     else
                         LineDataSet.Mode.CUBIC_BEZIER
                 }
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleStepped -> {
@@ -279,7 +279,7 @@ class LineChartDualAxisActivity : DemoBase(), OnSeekBarChangeListener, OnChartVa
                     else
                         LineDataSet.Mode.STEPPED
                 }
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleHorizontalCubic -> {
@@ -292,18 +292,18 @@ class LineChartDualAxisActivity : DemoBase(), OnSeekBarChangeListener, OnChartVa
                     else
                         LineDataSet.Mode.HORIZONTAL_BEZIER
                 }
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionTogglePinch -> {
                 chart!!.setPinchZoom(!chart!!.isPinchZoomEnabled)
 
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleAutoScaleMinMax -> {
                 chart!!.isAutoScaleMinMaxEnabled = !chart!!.isAutoScaleMinMaxEnabled
-                chart!!.notifyDataSetChanged()
+                chart?.notifyDataSetChanged()
             }
 
             R.id.animateX -> {
@@ -336,7 +336,7 @@ class LineChartDualAxisActivity : DemoBase(), OnSeekBarChangeListener, OnChartVa
         setData(seekBarX!!.progress, seekBarY!!.progress.toFloat())
 
         // redraw
-        chart!!.invalidate()
+        chart?.invalidate()
     }
 
     override fun saveToGallery() {
diff --git a/app/src/main/kotlin/info/appdev/chartexample/LineChartTimeActivity.kt b/app/src/main/kotlin/info/appdev/chartexample/LineChartTimeActivity.kt
index 160bc0067..b4fe5ef94 100644
--- a/app/src/main/kotlin/info/appdev/chartexample/LineChartTimeActivity.kt
+++ b/app/src/main/kotlin/info/appdev/chartexample/LineChartTimeActivity.kt
@@ -166,13 +166,13 @@ class LineChartTimeActivity : DemoBase(), OnSeekBarChangeListener {
                 chart!!.data!!.dataSets.forEach { set ->
                     set?.isDrawValues = !set.isDrawValues
                 }
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleHighlight -> {
                 if (chart!!.data != null) {
                     chart!!.data!!.isHighlightEnabled = !chart!!.data!!.isHighlightEnabled()
-                    chart!!.invalidate()
+                    chart?.invalidate()
                 }
             }
 
@@ -185,7 +185,7 @@ class LineChartTimeActivity : DemoBase(), OnSeekBarChangeListener {
                             set.setDrawFilled(true)
                     }
                 }
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleCircles -> {
@@ -195,7 +195,7 @@ class LineChartTimeActivity : DemoBase(), OnSeekBarChangeListener {
                     val set = iSet as LineDataSet
                     set.isDrawCirclesEnabled = !set.isDrawCirclesEnabled
                 }
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleCubic -> {
@@ -208,7 +208,7 @@ class LineChartTimeActivity : DemoBase(), OnSeekBarChangeListener {
                     else
                         set.lineMode = LineDataSet.Mode.CUBIC_BEZIER
                 }
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleStepped -> {
@@ -221,19 +221,19 @@ class LineChartTimeActivity : DemoBase(), OnSeekBarChangeListener {
                     else
                         set.lineMode = LineDataSet.Mode.STEPPED
                 }
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionTogglePinch -> {
                 if (chart!!.isPinchZoomEnabled) chart!!.setPinchZoom(false)
                 else chart!!.setPinchZoom(true)
 
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleAutoScaleMinMax -> {
                 chart!!.isAutoScaleMinMaxEnabled = !chart!!.isAutoScaleMinMaxEnabled
-                chart!!.notifyDataSetChanged()
+                chart?.notifyDataSetChanged()
             }
 
             R.id.animateX -> {
@@ -265,7 +265,7 @@ class LineChartTimeActivity : DemoBase(), OnSeekBarChangeListener {
         setData(seekBarX!!.progress)
 
         // redraw
-        chart!!.invalidate()
+        chart?.invalidate()
     }
 
     override fun saveToGallery() {
diff --git a/app/src/main/kotlin/info/appdev/chartexample/PerformanceLineChart.kt b/app/src/main/kotlin/info/appdev/chartexample/PerformanceLineChart.kt
index 0ff8d20d0..77f5f73e6 100644
--- a/app/src/main/kotlin/info/appdev/chartexample/PerformanceLineChart.kt
+++ b/app/src/main/kotlin/info/appdev/chartexample/PerformanceLineChart.kt
@@ -53,7 +53,7 @@ class PerformanceLineChart : DemoBase(), OnSeekBarChangeListener {
         seekBarValues!!.progress = 9000
 
         // don't forget to refresh the drawing
-        chart!!.invalidate()
+        chart?.invalidate()
     }
 
     private fun setData(count: Int, range: Float) {
@@ -113,7 +113,7 @@ class PerformanceLineChart : DemoBase(), OnSeekBarChangeListener {
         setData(count, 500f)
 
         // redraw
-        chart!!.invalidate()
+        chart?.invalidate()
     }
 
     public override fun saveToGallery() { /* Intentionally left empty */
diff --git a/app/src/main/kotlin/info/appdev/chartexample/PieChartActivity.kt b/app/src/main/kotlin/info/appdev/chartexample/PieChartActivity.kt
index fc135c24d..976fc8ccc 100644
--- a/app/src/main/kotlin/info/appdev/chartexample/PieChartActivity.kt
+++ b/app/src/main/kotlin/info/appdev/chartexample/PieChartActivity.kt
@@ -159,7 +159,7 @@ class PieChartActivity : DemoBase(), OnSeekBarChangeListener, OnChartValueSelect
         // undo all highlights
         chart!!.highlightValues(null)
 
-        chart!!.invalidate()
+        chart?.invalidate()
     }
 
     override fun onCreateOptionsMenu(menu: Menu?): Boolean {
@@ -180,26 +180,26 @@ class PieChartActivity : DemoBase(), OnSeekBarChangeListener, OnChartValueSelect
                 chart!!.data!!.dataSets.forEach {
                     it?.isDrawValues = !it.isDrawValues
                 }
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleIcons -> {
                 for (set in chart!!.data!!.getDataSets())
                     set?.isDrawIcons = !set.isDrawIcons
 
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleHole -> {
                 chart!!.isDrawHoleEnabled = !chart!!.isDrawHoleEnabled
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleMinAngles -> {
                 if (chart!!.minAngleForSlices == 0f) chart!!.setMinAngleForSlices(36f)
                 else chart!!.setMinAngleForSlices(0f)
-                chart!!.notifyDataSetChanged()
-                chart!!.invalidate()
+                chart?.notifyDataSetChanged()
+                chart?.invalidate()
             }
 
             R.id.actionToggleCurvedSlices -> {
@@ -211,22 +211,22 @@ class PieChartActivity : DemoBase(), OnSeekBarChangeListener, OnChartValueSelect
                 if (toSet && chart!!.isDrawSlicesUnderHoleEnabled) {
                     chart!!.setDrawSlicesUnderHole(false)
                 }
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionDrawCenter -> {
                 chart!!.setDrawCenterText(!chart!!.isDrawCenterTextEnabled)
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleXValues -> {
                 chart!!.setDrawEntryLabels(!chart!!.isDrawEntryLabelsEnabled)
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionTogglePercent -> {
                 chart!!.setUsePercentValues(!chart!!.isUsePercentValuesEnabled)
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.animateX -> {
diff --git a/app/src/main/kotlin/info/appdev/chartexample/PieChartRoundedActivity.kt b/app/src/main/kotlin/info/appdev/chartexample/PieChartRoundedActivity.kt
index bbf691e50..696768d54 100644
--- a/app/src/main/kotlin/info/appdev/chartexample/PieChartRoundedActivity.kt
+++ b/app/src/main/kotlin/info/appdev/chartexample/PieChartRoundedActivity.kt
@@ -165,7 +165,7 @@ class PieChartRoundedActivity : DemoBase(), OnSeekBarChangeListener, OnChartValu
         renderer.roundedCornerRadius = 30f
         dataSet.sliceSpace = renderer.roundedCornerRadius / 2
 
-        chart!!.invalidate()
+        chart?.invalidate()
     }
 
     override fun onCreateOptionsMenu(menu: Menu?): Boolean {
@@ -185,26 +185,26 @@ class PieChartRoundedActivity : DemoBase(), OnSeekBarChangeListener, OnChartValu
                 chart!!.data!!.dataSets.forEach {
                     it?.isDrawValues = !it.isDrawValues
                 }
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleIcons -> {
                 for (set in chart!!.data!!.getDataSets())
                     set?.isDrawIcons = !set.isDrawIcons
 
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleHole -> {
                 chart!!.isDrawHoleEnabled = !chart!!.isDrawHoleEnabled
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleMinAngles -> {
                 if (chart!!.minAngleForSlices == 0f) chart!!.setMinAngleForSlices(36f)
                 else chart!!.setMinAngleForSlices(0f)
-                chart!!.notifyDataSetChanged()
-                chart!!.invalidate()
+                chart?.notifyDataSetChanged()
+                chart?.invalidate()
             }
 
             R.id.actionToggleCurvedSlices -> {
@@ -216,22 +216,22 @@ class PieChartRoundedActivity : DemoBase(), OnSeekBarChangeListener, OnChartValu
                 if (toSet && chart!!.isDrawSlicesUnderHoleEnabled) {
                     chart!!.setDrawSlicesUnderHole(false)
                 }
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionDrawCenter -> {
                 chart!!.setDrawCenterText(!chart!!.isDrawCenterTextEnabled)
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleXValues -> {
                 chart!!.setDrawEntryLabels(!chart!!.isDrawEntryLabelsEnabled)
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionTogglePercent -> {
                 chart!!.setUsePercentValues(!chart!!.isUsePercentValuesEnabled)
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.animateX -> {
diff --git a/app/src/main/kotlin/info/appdev/chartexample/PiePolylineChartActivity.kt b/app/src/main/kotlin/info/appdev/chartexample/PiePolylineChartActivity.kt
index a850c6ea6..9d4bb5949 100644
--- a/app/src/main/kotlin/info/appdev/chartexample/PiePolylineChartActivity.kt
+++ b/app/src/main/kotlin/info/appdev/chartexample/PiePolylineChartActivity.kt
@@ -154,7 +154,7 @@ class PiePolylineChartActivity : DemoBase(), OnSeekBarChangeListener, OnChartVal
         // undo all highlights
         chart!!.highlightValues(null)
 
-        chart!!.invalidate()
+        chart?.invalidate()
     }
 
     override fun onCreateOptionsMenu(menu: Menu?): Boolean {
@@ -174,19 +174,19 @@ class PiePolylineChartActivity : DemoBase(), OnSeekBarChangeListener, OnChartVal
                 chart!!.data!!.dataSets.forEach {
                     it?.isDrawValues = !it.isDrawValues
                 }
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleHole -> {
                 chart!!.isDrawHoleEnabled = !chart!!.isDrawHoleEnabled
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleMinAngles -> {
                 if (chart!!.minAngleForSlices == 0f) chart!!.setMinAngleForSlices(36f)
                 else chart!!.setMinAngleForSlices(0f)
-                chart!!.notifyDataSetChanged()
-                chart!!.invalidate()
+                chart?.notifyDataSetChanged()
+                chart?.invalidate()
             }
 
             R.id.actionToggleCurvedSlices -> {
@@ -198,22 +198,22 @@ class PiePolylineChartActivity : DemoBase(), OnSeekBarChangeListener, OnChartVal
                 if (toSet && chart!!.isDrawSlicesUnderHoleEnabled) {
                     chart!!.setDrawSlicesUnderHole(false)
                 }
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionDrawCenter -> {
                 chart!!.setDrawCenterText(!chart!!.isDrawCenterTextEnabled)
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleXValues -> {
                 chart!!.setDrawEntryLabels(!chart!!.isDrawEntryLabelsEnabled)
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionTogglePercent -> {
                 chart!!.setUsePercentValues(!chart!!.isUsePercentValuesEnabled)
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.animateX -> {
diff --git a/app/src/main/kotlin/info/appdev/chartexample/RadarChartActivity.kt b/app/src/main/kotlin/info/appdev/chartexample/RadarChartActivity.kt
index eccadb908..d72faf595 100644
--- a/app/src/main/kotlin/info/appdev/chartexample/RadarChartActivity.kt
+++ b/app/src/main/kotlin/info/appdev/chartexample/RadarChartActivity.kt
@@ -139,7 +139,7 @@ class RadarChartActivity : DemoBase() {
         colorList.add(Color.rgb(240, 255, 240))
         colorList.add(Color.rgb(250, 255, 250))
         chart!!.setLayerColorList(colorList)
-        chart!!.invalidate()
+        chart?.invalidate()
     }
 
     override fun onCreateOptionsMenu(menu: Menu?): Boolean {
@@ -160,44 +160,44 @@ class RadarChartActivity : DemoBase() {
                     it?.isDrawValues = !it.isDrawValues
                 }
 
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleHighlight -> {
                 if (chart!!.data != null) {
                     chart!!.data!!.isHighlightEnabled = !chart!!.data!!.isHighlightEnabled()
-                    chart!!.invalidate()
+                    chart?.invalidate()
                 }
             }
 
             R.id.actionToggleRotate -> {
                 chart!!.isRotationEnabled = !chart!!.isRotationEnabled
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleFilled -> {
                 chart!!.data!!.dataSets.forEach { set ->
                     set?.setDrawFilled(!set.isDrawFilledEnabled)
                 }
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleHighlightCircle -> {
                 chart!!.data!!.dataSets.forEach { set ->
                     set.isDrawHighlightCircleEnabled = !set.isDrawHighlightCircleEnabled
                 }
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleXLabels -> {
                 chart!!.xAxis.isEnabled = !chart!!.xAxis.isEnabled
-                chart!!.notifyDataSetChanged()
-                chart!!.invalidate()
+                chart?.notifyDataSetChanged()
+                chart?.invalidate()
             }
 
             R.id.actionToggleYLabels -> {
                 chart!!.yAxis.isEnabled = !chart!!.yAxis.isEnabled
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.animateX -> {
diff --git a/app/src/main/kotlin/info/appdev/chartexample/RealtimeLineChartActivity.kt b/app/src/main/kotlin/info/appdev/chartexample/RealtimeLineChartActivity.kt
index fa6435822..37ab52739 100644
--- a/app/src/main/kotlin/info/appdev/chartexample/RealtimeLineChartActivity.kt
+++ b/app/src/main/kotlin/info/appdev/chartexample/RealtimeLineChartActivity.kt
@@ -100,7 +100,7 @@ class RealtimeLineChartActivity : DemoBase(), OnChartValueSelectedListener {
             data.notifyDataChanged()
 
             // let the chart know it's data has changed
-            chart!!.notifyDataSetChanged()
+            chart?.notifyDataSetChanged()
 
             // limit the number of visible entries
             chart!!.setVisibleXRangeMaximum(120f)
diff --git a/app/src/main/kotlin/info/appdev/chartexample/ScatterChartActivity.kt b/app/src/main/kotlin/info/appdev/chartexample/ScatterChartActivity.kt
index 9641236e1..74f06d356 100644
--- a/app/src/main/kotlin/info/appdev/chartexample/ScatterChartActivity.kt
+++ b/app/src/main/kotlin/info/appdev/chartexample/ScatterChartActivity.kt
@@ -133,7 +133,7 @@ class ScatterChartActivity : DemoBase(), OnSeekBarChangeListener, OnChartValueSe
         data.setValueTypeface(tfLight)
 
         chart!!.setData(data)
-        chart!!.invalidate()
+        chart?.invalidate()
     }
 
     override fun onCreateOptionsMenu(menu: Menu?): Boolean {
@@ -153,25 +153,25 @@ class ScatterChartActivity : DemoBase(), OnSeekBarChangeListener, OnChartValueSe
                 chart!!.data!!.dataSets.forEach { set ->
                     set?.isDrawValues = !set.isDrawValues
                 }
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleHighlight -> {
                 if (chart!!.data != null) {
                     chart!!.data!!.isHighlightEnabled = !chart!!.data!!.isHighlightEnabled()
-                    chart!!.invalidate()
+                    chart?.invalidate()
                 }
             }
 
             R.id.actionTogglePinch -> {
                 chart!!.setPinchZoom(!chart!!.isPinchZoomEnabled)
 
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleAutoScaleMinMax -> {
                 chart!!.isAutoScaleMinMaxEnabled = !chart!!.isAutoScaleMinMaxEnabled
-                chart!!.notifyDataSetChanged()
+                chart?.notifyDataSetChanged()
             }
 
             R.id.animateX -> {
diff --git a/app/src/main/kotlin/info/appdev/chartexample/ScrollViewActivity.kt b/app/src/main/kotlin/info/appdev/chartexample/ScrollViewActivity.kt
index 1c51ba1c5..dfde6c005 100644
--- a/app/src/main/kotlin/info/appdev/chartexample/ScrollViewActivity.kt
+++ b/app/src/main/kotlin/info/appdev/chartexample/ScrollViewActivity.kt
@@ -59,7 +59,7 @@ class ScrollViewActivity : DemoBase() {
         val data = BarData(set)
 
         chart!!.setData(data)
-        chart!!.invalidate()
+        chart?.invalidate()
         chart!!.animateY(800)
     }
 
diff --git a/app/src/main/kotlin/info/appdev/chartexample/StackedBarActivity.kt b/app/src/main/kotlin/info/appdev/chartexample/StackedBarActivity.kt
index fa05b1968..430a952aa 100644
--- a/app/src/main/kotlin/info/appdev/chartexample/StackedBarActivity.kt
+++ b/app/src/main/kotlin/info/appdev/chartexample/StackedBarActivity.kt
@@ -125,7 +125,7 @@ class StackedBarActivity : DemoBase(), OnSeekBarChangeListener, OnChartValueSele
             set1 = chart!!.data!!.getDataSetByIndex(0) as BarDataSet
             set1.entries  = values
             chart!!.data!!.notifyDataChanged()
-            chart!!.notifyDataSetChanged()
+            chart?.notifyDataSetChanged()
         } else {
             set1 = BarDataSet(values, "Statistics Vienna 2014")
             set1.isDrawIcons = false
@@ -143,7 +143,7 @@ class StackedBarActivity : DemoBase(), OnSeekBarChangeListener, OnChartValueSele
         }
 
         chart!!.setFitBars(true)
-        chart!!.invalidate()
+        chart?.invalidate()
     }
 
     override fun onCreateOptionsMenu(menu: Menu?): Boolean {
@@ -163,38 +163,38 @@ class StackedBarActivity : DemoBase(), OnSeekBarChangeListener, OnChartValueSele
                 chart!!.data!!.dataSets.forEach {
                     it?.isDrawValues = !it.isDrawValues
                 }
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleIcons -> {
                 chart!!.data!!.dataSets.forEach { set ->
                     set?.isDrawIcons = !set.isDrawIcons
                 }
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleHighlight -> {
                 if (chart!!.data != null) {
                     chart!!.data!!.isHighlightEnabled = !chart!!.data!!.isHighlightEnabled()
-                    chart!!.invalidate()
+                    chart?.invalidate()
                 }
             }
 
             R.id.actionTogglePinch -> {
                 chart!!.setPinchZoom(!chart!!.isPinchZoomEnabled)
 
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleAutoScaleMinMax -> {
                 chart!!.isAutoScaleMinMaxEnabled = !chart!!.isAutoScaleMinMaxEnabled
-                chart!!.notifyDataSetChanged()
+                chart?.notifyDataSetChanged()
             }
 
             R.id.actionToggleBarBorders -> {
                 for (set in chart!!.data!!.dataSets) (set as BarDataSet).barBorderWidth = if (set.barBorderWidth == 1f) 0f else 1f
 
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.animateX -> {
diff --git a/app/src/main/kotlin/info/appdev/chartexample/StackedBarActivityNegative.kt b/app/src/main/kotlin/info/appdev/chartexample/StackedBarActivityNegative.kt
index baf8dd1a0..e3d1d74b5 100644
--- a/app/src/main/kotlin/info/appdev/chartexample/StackedBarActivityNegative.kt
+++ b/app/src/main/kotlin/info/appdev/chartexample/StackedBarActivityNegative.kt
@@ -110,7 +110,7 @@ class StackedBarActivityNegative : DemoBase(), OnChartValueSelectedListener {
         val data = BarData(set)
         data.barWidth = 8.5f
         chart!!.setData(data)
-        chart!!.invalidate()
+        chart?.invalidate()
     }
 
     override fun onCreateOptionsMenu(menu: Menu?): Boolean {
@@ -131,7 +131,7 @@ class StackedBarActivityNegative : DemoBase(), OnChartValueSelectedListener {
                 chart!!.data!!.dataSets.forEach {
                     it?.isDrawValues = !it.isDrawValues
                 }
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleIcons -> {
@@ -139,13 +139,13 @@ class StackedBarActivityNegative : DemoBase(), OnChartValueSelectedListener {
                     set?.isDrawIcons = !set.isDrawIcons
                 }
 
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleHighlight -> {
                 if (chart!!.data != null) {
                     chart!!.data!!.isHighlightEnabled = !chart!!.data!!.isHighlightEnabled()
-                    chart!!.invalidate()
+                    chart?.invalidate()
                 }
             }
 
@@ -156,12 +156,12 @@ class StackedBarActivityNegative : DemoBase(), OnChartValueSelectedListener {
                     chart!!.setPinchZoom(true)
                 }
 
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.actionToggleAutoScaleMinMax -> {
                 chart!!.isAutoScaleMinMaxEnabled = !chart!!.isAutoScaleMinMaxEnabled
-                chart!!.notifyDataSetChanged()
+                chart?.notifyDataSetChanged()
             }
 
             R.id.actionToggleBarBorders -> {
@@ -169,7 +169,7 @@ class StackedBarActivityNegative : DemoBase(), OnChartValueSelectedListener {
                     (set as BarDataSet).barBorderWidth = if (set.barBorderWidth == 1f) 0f else 1f
                 }
 
-                chart!!.invalidate()
+                chart?.invalidate()
             }
 
             R.id.animateX -> {
diff --git a/app/src/main/kotlin/info/appdev/chartexample/listviewitems/PieChartItem.kt b/app/src/main/kotlin/info/appdev/chartexample/listviewitems/PieChartItem.kt
index 3a8fad1fd..2475f049e 100644
--- a/app/src/main/kotlin/info/appdev/chartexample/listviewitems/PieChartItem.kt
+++ b/app/src/main/kotlin/info/appdev/chartexample/listviewitems/PieChartItem.kt
@@ -64,17 +64,18 @@ class PieChartItem(cd: ChartData<*>, c: Context) : ChartItem(cd) {
         // set data
         holder.chart!!.setData(chartData as PieData?)
 
-        val l = holder.chart!!.legend
-        l.verticalAlignment = Legend.LegendVerticalAlignment.TOP
-        l.horizontalAlignment = Legend.LegendHorizontalAlignment.RIGHT
-        l.orientation = Legend.LegendOrientation.VERTICAL
-        l.setDrawInside(false)
-        l.yEntrySpace = 0f
-        l.yOffset = 0f
+        holder.chart?.legend?.apply {
+            verticalAlignment = Legend.LegendVerticalAlignment.TOP
+            horizontalAlignment = Legend.LegendHorizontalAlignment.RIGHT
+            orientation = Legend.LegendOrientation.VERTICAL
+            setDrawInside(false)
+            yEntrySpace = 0f
+            yOffset = 0f
+        }
 
         // do not forget to refresh the chart
         // holder.chart.invalidate();
-        holder.chart!!.animateY(900)
+        holder.chart?.animateY(900)
 
         return convertView
     }